Electromechanical grating display system with segmented waveplate

ABSTRACT

A display system, including: a light source providing illumination; a linear array of electromechanical grating devices of at least two individually operable devices receiving the illumination wherein a grating period is oriented at a predetermined angle with respect to an axis of the linear array wherein the angle is large enough to separate diffracted light beams prior to a projection lens system for projecting light onto a screen; a polarization sensitive element that passes diffracted light beams according to their polarization state; a segmented waveplate for altering the polarization state of a discrete number of selected diffracted light beams wherein the segmented waveplate is located between the linear array and the polarization sensitive element, a scanning element for moving the selectively passed diffracted light beams on the screen; and a controller for providing a data stream to the individually operable devices.

FIELD OF THE INVENTION

This invention relates to a display system with a linear array ofelectromechanical grating devices that is scanned in order to generate atwo-dimensional image. More particularly, the invention relates to anelectromechanical grating display system that uses a segmented waveplateto select diffracted light beams for projection onto a screen.

BACKGROUND OF THE INVENTION

Spatial light modulators consisting of an array of high-speedelectromechanical phase gratings are important for a variety of systems,including display, optical processing, printing, optical data storageand spectroscopy. Each of the devices on the array can be individuallycontrolled to selectively reflect or diffract an incident light beaminto a number of light beams of discrete orders. Depending on theapplication, one or more of the modulated light beams may be collectedand used by the optical system.

Electromechanical phase gratings can be formed in metallized elastomergels. The electrodes below the elastomer are patterned so that theapplication of a voltage deforms the elastomer producing a nearlysinusoidal phase grating. These types of devices have been successfullyused in color projection displays; see Metallized viscoelastic controllayers for light-valve projection displays, by Brinker et al., Displays16, 1994, pp. 13-20, and Full-colour diffraction-based optical systemfor light-valve projection displays, by

Roder et al., Displays 16, 1995, pp. 27-34.

An electromechanical phase grating with a much faster response time canbe made of suspended micromechanical ribbon elements, as described inU.S. Pat. No. 5,311,360, issued May 10, 1994 to Bloom et al., entitledMethod and Apparatus for Modulating a Light Beam. This device, alsoknown as a grating light valve (GLV), can be fabricated with CMOS-likeprocesses on silicon. For display or printing, linear arrays of GLVdevices can be used with a scanning Schlieren optical system asdescribed in U.S. Pat. No. 5,982,553, issuedNov. 9, 1999 to Bloom etal., entitled Display Device Incorporating One-Dimensional GratingLight-Valve Array. Alternatively, an interferometric optical system canbe used to display an image as disclosed in U.S. Pat. No. 6,088,102,issued Jul. 11, 2000 to Manhart, entitled Display Apparatus IncludingGrating Light-Valve Array and Interferometric Optical System. In thescanning Schlieren display system of Bloom et al. '553, the plane ofdiffraction that contains the diffracted light beams is parallel to theaxis of the linear GLV array because the grating period is parallel tothe axis. This feature increases the cost and complexity of the displaysystem. Specifically, efficient collection of the primary diffractedlight beams requires at least one dimension of the optical elements tobe significantly larger than the extent of the linear GLV array.Furthermore, the diffracted and reflected light beams overlap spatiallythroughout most of the optical system. Separation of diffracted lightfrom reflected light is accomplished in close proximity to a Fourierplane of the Schlieren optical system. However, the Fourier plane isalso usually the preferred location of a scanning mirror for producing atwo-dimensional image.

Recently, a linear array of electromechanical conformal grating deviceswas disclosed by Kowarz, in U.S. Ser. No. 09/491,354, filed Jan. 26,2000. For this class of devices, it is preferable to have the gratingperiod perpendicular to the axis of the linear array. The diffractedlight beams are then spatially separated throughout most of the opticalsystem. In U.S. Ser. No. 09/491,354, it was mentioned that a simplifieddisplay system can be designed based on this type of spatial lightmodulator. However, no specific description of the display system wasgiven. There is a need therefore for a scanning display system thatutilizes a linear array of electromechanical conformal grating devices.Furthermore, there is a need for a display system that is simpler andless costly than other known systems.

SUMMARY OF THE INVENTION

The need is met according to the present invention by providing adisplay system that includes: a light source providing illumination; alinear array of electromechanical grating devices of at least twoindividually operable devices receiving the illumination wherein agrating period is oriented at a predetermined angle with respect to anaxis of the linear array wherein the angle is large enough to separatediffracted light beams prior to a projection lens system for projectinglight onto a screen; a polarization sensitive element that passesdiffracted light beams according to their polarization state; asegmented waveplate for altering the polarization state of a discretenumber of selected diffracted light beams wherein the segmentedwaveplate is located between the linear array and the polarizationsensitive element; a scanning element for moving the selectively passeddiffracted light beams on the screen; and a controller for providing adata stream to the individually operable devices.

The present invention has several advantages, including: 1) improvementin contrast by eliminating reflections from the projection lens, becausesuch reflections are directed away from the screen; 2) reduction in sizeof the scanning mirror, because now the scanning mirror can be placeddirectly at the Fourier plane; 3) increase in design flexibility,because now selection and separation of diffracted orders can take placealmost anywhere in the system, rather than solely at the Fourier plane;and 4) reduction in size of lenses and other optical elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, partially cut-away view of a spatial lightmodulator with electromechanical conformal grating devices, showing twodevices in a linear array;

FIG. 2 is a top view of a spatial light modulator with electromechanicalconformal grating devices, showing four individually operable devices ina linear array;

FIGS. 3a and 3 b are cross-sectional views through line III—III in FIG.2, showing the operation of an electromechanical conformal gratingdevice in an unactuated state and an actuated state, respectively;

FIGS. 4a and 4 b show the operation of a conventional electromechanicaltwo-level grating device in an unactuated state and an actuated state,respectively;

FIG. 5 is a top view of a spatial light modulator with conventional GLVdevices, showing five individually operable devices in a linear arraywith deformable ribbon elements oriented perpendicular to the axis ofthe array and the grating period oriented parallel to the axis;

FIG. 6 is a top view of a spatial light modulator with conventional GLVdevices, showing five individually operable devices in a linear arraywith deformable ribbon elements oriented parallel to the axis of thearray and the grating period oriented perpendicular to the axis;

FIG. 7 is a schematic illustrating a prior art, line-scanned Schleirendisplay system that includes a light source, illumination optics, alinear array of conventional GLV devices, a projection lens, a scanningmirror, a controller, and a turning mirror located at the Fourier planeof the projection lens;

FIG. 8 is a schematic illustrating a line-scanned display system thatincludes a light source, illumination optics, a linear array ofelectromechanical conformal grating devices, a projection lens, ascanning mirror, a controller, and a turning mirror located between thelinear array and the projection lens;

FIG. 9 shows a linear array of electromechanical conformal gratingdevices illuminated by a line of light;

FIG. 10 is a view of the projection screen that illustrates theformation of a two-dimensional image by scanning a line image across thescreen;

FIGS. 11a-11 h are density plots of the light distribution in differentplanes of a prior art, line-scanned Schleiren display system in whichthe modulator is a linear array of conventional GLV devices withdeformable ribbon elements oriented perpendicular to the axis of thearray;

FIGS. 12a-12 h are density plots of the light distribution in differentplanes of a line-scanned display system in which the modulator is alinear array of electromechanical conformal grating devices;

FIG. 13 is a schematic illustrating an embodiment of the display systemin which the turning mirror is placed between the first projection lensand the scanning mirror, and an intermediate image plane is formed inthe system;

FIG. 14 is a schematic illustrating an embodiment of the display systemthat includes a polarization beamsplitter and a segmented waveplate forseparating +1^(st) and −1^(st) order light beams from the 0^(th) orderlight beam;

FIG. 15a shows the segmented waveplate for order separation;

FIG. 15b shows an alternate version of the segmented waveplate for orderseparation;

FIG. 16 is a schematic illustrating a color, line-scanned display systemthat includes a three-color light source, illumination optics, a colorcombination cube, three linear arrays of electromechanical conformalgrating devices, three projection lenses, a scanning mirror, apolarization beamsplitter, and three segmented waveplates for separating+1^(st) and −1^(st) order light beams from 0^(th) order light beams;

FIG. 17 is a schematic illustrating a color, line-scanned display systemwith a single multi-color segmented waveplate;

FIG. 18 shows the multi-color segmented waveplate for order separation;

FIG. 19 is a schematic illustrating an alternate embodiment of a color,line-scanned display system with three segmented waveplates; and

FIG. 20 is a schematic illustrating a printer system that includes apolarization beamsplitter and a segmented waveplate for separating+1^(st) and −1^(st) order light beams from the 0^(th) order light beam.

DETAILED DESCRIPTION OF THE INVENTION

The structure and operation of an electromechanical conformal gratingdevice is illustrated in FIGS. 1-3. FIG. 1 shows two side-by-sideconformal grating devices 5 a and 5 b in an unactuated state. In thisembodiment, the devices can be operated by the application of anelectrostatic force. The grating devices 5 a and 5 b are formed on topof a substrate 10 covered by a bottom conductive layer 12 which acts asan electrode to actuate the conformal grating devices 5 a and 5 b. Thebottom conductive layer 12 is covered by a dielectric protective layer14 followed by a standoff layer 16 and a spacer layer 18. On top of thespacer layer 18, a ribbon layer 20 is formed which is covered by areflective layer 22. The reflective layer 22 is also a conductor inorder to provide electrodes for the actuation of the conformal gratingdevices 5 a and 5 b. The reflective and conductive layer 22 is patternedto provide electrodes to the two conformal grating devices 5 a and 5 b.The ribbon layer 20 preferably comprises a material with a sufficienttensile stress to provide a large restoring force. Each of the twoconformal grating devices 5 a and 5 b has an associated elongated ribbonelement 23 a and 23 b, respectively, patterned from the reflective andconductive layer 22 and the ribbon layer 20. The elongated ribbonelements 23 a and 23 b are supported by end supports 24 a and 24 bformed from the spacer layer 18 and by one or more intermediate supports27 that are uniformly separated in order to form four equal-widthchannels 25. The elongated ribbon elements 23 a and 23 b are secured tothe end supports 24 a and 24 b and to the intermediate supports 27. Aplurality of square standoffs 29 is patterned at the bottom of thechannels 25 from the standoff layer 16. These standoffs 29 reduce thepossibility of the ribbon elements 23 a and 23 b sticking when actuated.

A top view of a four-device linear array of conformal grating devices 6a, 6 b, 6 c, and 5 d is shown in FIG. 2. The elongated ribbon elements23 a, 23 b, 23 c, and 23 d are depicted partially removed over theportion of the diagram below the line III—III in order to show theunderlying structure. For best optical performance and maximum contrast,the intermediate supports 27 must be completely hidden below theelongated ribbon elements 23 a, 23 b, 23 c and 23 d. Therefore, whenviewed from the top, the intermediate supports 27 must not be visible inthe gaps 28 between the conformal grating devices 5 a-5 d. Here each ofthe conformal grating devices 5 a-5 d has three intermediate supports 27with four equal-width channels 25. The center-to-center separation A ofthe intermediate supports 27 defines the period of the conformal gratingdevices 5 a-5 d in the actuated state. The elongated ribbon elements 23a-23 d are mechanically and electrically isolated from one another,allowing independent operation of the four conformal grating devices 5a-5 d. The bottom conductive layer 12 of FIG. 1 can be common to all ofthe devices.

FIG. 3a is a side view, through line III—III of FIG. 2, of two channelsof the conformal grating device 5 b (as shown and described in FIG. 1)in the unactuated state. FIG. 3b shows the same view of the actuatedstate. For operation of the device, an attractive electrostatic force isproduced by applying a voltage difference between the bottom conductivelayer 12 and the reflective, conducting layer 22 of the elongated ribbonelement 23 b. In the unactuated state (see FIG. 3a), with no voltagedifference, the ribbon element 23 b is suspended flat between the endsupports 24 a and 24 b. In this state, an incident light beam 30 isprimarily diffracted into a 0th order light beam 32 in the mirrordirection. To obtain the actuated state, a voltage is applied to theconformal grating device 6 b, which deforms the elongated ribbon element23 b and produces a partially conformal grating with period Λ. FIG. 3bshows the conformal grating device 5 b (as shown and described inFIG. 1) in the fully actuated state with the elongated ribbon element 23b in contact with the standoffs 29. The height difference between thebottom of element 23 b and the top of the standoffs 29 is chosen to beapproximately ¼ of the wavelength λ of the incident light. The optimumheight depends on the specific shape of the actuated device. In theactuated state, the incident light beam 30 is primarily diffracted intothe +1st order light beam 35 a and −1st order light beam 36 b, withadditional light diffracted into the +2nd order 36 a and −2nd order 36b. A small amount of light is diffracted into even higher orders andsome is diffracted into the 0th order. One or more of the diffractedbeams can be collected and used by the optical system, depending on theapplication. When the applied voltage is removed, the forces due to thetensile stress and bending restores the ribbon element 23 b to itsoriginal unactuated state.

A linear array of conformal grating devices is formed by arranging thedevices as illustrated in FIGS. 1-3 with the direction of the gratingperiod A along the y direction and perpendicular to the axis of thearray (i.e., the x direction). For a given incident angle, the planescontaining the various diffracted light beams are distinct. These planesall intersect in a line at the linear array. Even with a large lineararray consisting, possibly, of several thousand devices illuminated by anarrow line of light, the diffracted light beams become spatiallyseparated over a relatively short distance. This feature simplifies theoptical system design and enables feasible designs in which theseparation of diffracted light beams can be done spatially withoutSchlieren optics.

A conventional Grating Light Valve (GLV) is shown in FIGS. 4a and 4 b.FIG. 4a depicts the ribbon structure of the device in the unactuatedstate and FIG. 4b in the actuated state. For operation of the device, anattractive electrostatic force is produced by a voltage differencebetween the bottom conductive layer 42 and the reflective and conductivelayer 48 atop the ribbon element 46. In the unactuated state, with novoltage difference, all of the ribbon elements 46 in the GLV device aresuspended above the substrate 40 at the same height. In this state, anincident light beam 54 is primarily reflected as from a mirror to form a0th order diffracted light beam 55. To obtain the actuated state (seeFIG. 4b), a voltage is applied to every other ribbon element 46producing a grating. In the fully actuated state, every other ribbonelement 46 is in contact with the protective layer 44. When the heightdifference between adjacent ribbon elements is ¼ of the wavelength of anincident light beam 56, the light beam is primarily diffracted into a+1st order light beam 57 and a −1st order light beam 58. One or more ofthe diffracted beams can be collected and used by an optical system,depending on the application. When the applied voltage is removed, theforce due to the tensile stress restores the ribbon elements 46 to theiroriginal unactuated state (see FIG. 4a).

The table below summarizes the key differences between a conformalgrating device and a conventional GLV for a single device of each type.

Conformal grating device Conventional GLV # of moving ribbons 1 3-6 # ofstationary ribbons none 3-6 Number of channels >5 1 Grating perioddirection Parallel to ribbon length Perpendicular to ribbon lengthGrating profile Smoothly varying Square (binary)

It should be noted that the parameters above pertain to the preferredforms of each of the devices.

In a linear array made from conventional GLV devices, the ribbonelements are usually all arranged parallel to each other. FIG. 5 showsthe top view of a portion of such a linear array. In this example, eachof 5 devices 45 a, 45 b, 45 c, 45 d and 45 e contains 4 movable ribbonelements 46 a that are electrically connected to each other and 4stationary ribbon elements 46 b that are connected to ground. Theapplication of a voltage to a device causes the movable ribbon elements46 a belonging to that device to actuate in unison into the channel 50.The grating period Λformed by the actuated ribbons is parallel to theaxis of the array and perpendicular to the length of the ribbon elements46 a and 46 b. The diffracted light beams then overlap spatially over arelatively long distance.

As a comparative example between the two types of linear arrays, let usconsider an array of conformal grating devices that is 4 cm long (2000devices 20 μm wide) illuminated by a 100 μm wide line of light. Fordevices with a period chosen such that the diffracted orders areangularly separated by 1 degree, the orders will become spatiallyseparated in approximately 6 mm. This rapid separation of diffractedorders occurs because the grating period is perpendicular to the axis ofthe linear array of conformal grating devices and is parallel to thelength of the ribbon elements. A similar 4 cm linear array of prior artGLV devices with a 4 degree angular separation between diffracted orderswould require at least 60 cm for spatial separation, without the use ofa Schlieren optical system. This relatively slow order separation occursbecause the grating period is parallel to the axis of the linear arrayof GLV devices.

A linear array of GLV devices can also be constructed with the ribbonelements perpendicular to the axis of the array as illustrated in FIG.6. Each of the 5 devices 62 a, 62 b, 62 c, 62 d and 62 e is individuallyoperable and has its own channel 60 a, 60 b, 60 c, 60 d and 60 e. Forsuch a GLV array, the grating period Λis perpendicular to the axis ofthe array and the diffracted light beams become spatially separated overa relatively short distance. However, this type of GLV array suffersfrom the existence of significant gaps between devices that cause somepixelation in the display.

FIG. 7 shows a GLV-based display system of the prior art that has aSchlieren optical system. The linear array 85 consists of GLV devices ofthe type shown in FIG. 5. Light is emitted from a source 70 and passesthrough a spherical lens 72 and a cylindrical lens 74 before hitting aturning mirror 82. The turning mirror 82 is placed at the Fourier(focal) plane of a projection lens system 75. Although only a singlelens element is shown, in practice, the projection lens system willconsist of multiple elements. Light reflected by the turning mirror 82is focused by the projection lens system 75 into a line illuminating thelinear array 85. A small portion of the illumination that strikes theprojection lens system 75 will be reflected. In order to avoid areduction in the contrast of the display system from such reflections,the projection lens system 75 needs to have very good optical coatingsand/or needs to be used off-axis. The GLV devices of the linear array 85are selectively activated by the controller 80 to correspond to a lineof pixels. If a particular device of the array is actuated byapplication of a voltage to the ribbon elements, it diffracts lightprimarily into +1st order and −1st order light beams. If a particulardevice is not actuated, it diffracts light primarily into the 0th orderlight beam. These three primary light beams are collected by the sameprojection lens 75, which focuses the three light beams into distinctspots at the Fourier plane. The 0th order light beam hits the turningmirror 82 and is reflected towards the light source 70. The +1st and−1st order light beams pass above and below the turning mirror 82 andstrike a scanning mirror 77 that sweeps the light beams across a screen90 to form a viewable two-dimensional image. Higher-order light beamsalso show up as spots in the Fourier plane and can be blocked fromreaching the screen 90 by a stop in the Fourier plane (not shown). Thecontroller 80 synchronizes the sweep of the scanning mirror 77 with theactuation of the devices of the linear array 85.

In the prior art display system of FIG. 7, in order to effectivelyseparate the +1st and −1st order light beams from the 0th order lightbeam, the turning mirror 82 must be placed near the Fourier plane of theprojection lens system 75, i.e., it must be located at approximately thefocal distance f from the lens. However, this location is also best forplacing the scanning mirror 77 because the +1st and −1st order lightbeams are tightly focused here, allowing for a reduction in the size andweight of the scanning mirror 77.

FIGS. 8-10 illustrate a display system with a turning mirror 82 placedbetween the linear array 85 and the projection lens system 75. Lightemitted by source 70 is conditioned by a spherical lens 72 and acylindrical lens 74 before hitting the turning mirror 82 and focusing onthe linear array 85. In this system, the axis of the cylindrical lens 74is rotated 90 degrees with respect to the cylindrical lens 74 in FIG. 7.By placing the turning mirror 82 between the linear array 85 and theprojection lens system 75, the contrast-reducing reflections of theprior art system of FIG. 7 are eliminated because the illuminating lightbeam never passes through the projection lens system 75. FIG. 9 showsthe linear array 85 illuminated by a line of light 88. In thisparticular example there are 17 electromechanical conformal gratingdevices shown. In practice, there would be hundreds or thousands ofdevices. The controller 80 selects the devices to be actuated based onthe desired pixel pattern for a given line of a two-dimensional image.If a particular device is not actuated, it diffracts the incident lightbeam primarily into the 0th order light beam, which subsequently hitsthe turning mirror 82 and is reflected towards the source 70. If thedevice is actuated, it diffracts the incident light beams primarily into+1st order and −1st order light beams. These two first-order diffractedlight beams pass around the turning mirror 82 and are projected on thescreen 90 by the projection lens system 75. Higher-order diffractedlight beams can be blocked by the addition of a stop 83. The scanningmirror 77 sweeps the line image across the screen 90 to form thetwo-dimensional image. Preferably, the scanning mirror 77 is placed nearthe Fourier plane of the projection lens system 75. FIG. 10 is a viewfacing the screen 90 showing the formation of a two-dimensional imagefrom a series of 1080 sequential line scans.

Clearly, there are two kinds of diffracted light beams in this displaysystem: those that are blocked by obstructing elements from reaching thescreen 90 and those that pass around obstructing elements to form animage on the screen 90. In this particular system, the obstructingelements are the turning mirror 82 that blocks the 0th order light beamand the stops 83 that block the ±2nd, ±3rd, ±4th . . . orders of light.As will be explained later, according to the present invention, thecombination of a polarization sensitive element, such as a beamsplitter,and a segmented waveplate can be used as an alternate method forchoosing the diffracted light beams that are allowed to reach the screen90.

The linear array 85 is preferably constructed of electromechanicalconformal grating devices of the type shown in FIGS. 1-3. It may also beconstructed of GLV devices of the type shown in FIG. 6, or of otherkinds of electromechanical grating devices. However, in order to placethe turning mirror 82 before the projection lens system 75, the gratingperiod Λmust be rotated at a sufficiently large angle with respect tothe long axis of the linear array 85. For the electromechanicalconformal grating devices of FIGS. 1-3 and the GLV devices of FIG. 6,this angle is 90 degrees. A lesser angle can also be used so long as thediffracted orders become separated before reaching the projection lenssystem 75. It is impractical, however, to make this type of displaysystem with no rotation between the grating period and the axis of thelinear array 85. Therefore, a conventional linear array of GLV devicesof the type shown in FIG. 5 cannot be used with this kind of system.

The significant differences between the display system of the prior art(FIG. 7) and the display system of FIG. 8 can be understood by examiningthe propagation of the diffracted light beams throughout the twosystems. FIGS. 11a-11 h show the amplitude of the diffracted light beamsalong several parallel planes between the linear array 85 and the screen90 for the prior art system of FIG. 7. In this modeled example, the lenshas a focal length f of 50 mm, the linear array is 1 cm long. D refersto the distance between the linear array 85 to the plane of interest. Asthe diffracted light beams emerge from the linear array 85, they beginto spread along the direction of the axis of the linear array asillustrated in FIGS. 11a-11 d. The interference between the variousdiffracted beams causes a rapid variation in the intensity known tothose skilled in the art as tilt fringes. At the plane just before theprojection lens (see FIG. 11d), the diffracted light beams have spreadto about twice the length of the linear array. The lens must be largeenough to avoid truncating the diffracted light beams to be projected onthe screen, which are the −1st and +1st order light beams in this case.After passing through the projection lens system 75, the beams begin tofocus. At a distance of D=90 mm from the linear array 85, the variousdiffracted orders are spatially separated. Distinct spots are visiblethat correspond to the +3rd, +2nd, +1st, 0th , −1st, −2nd and −3rdorders (see FIG. 11g). At the Fourier plane (D=100 mm), the turningmirror 82 blocks the 0th order light beam and a stop blocks the +3rd,+2nd, −2nd and −3rd orders. The +1st and −1st order light beams continuetowards the screen 90 where they overlap spatially to form the lineimage. It is important to note that the various order light beams areonly spatially separated near the Fourier plane (near D=100 mm).Therefore, only the vicinity of this plane is available for separatingthe +1st and −1st order light beams from the rest of the diffractedorders.

FIGS. 12a-12 h show the amplitude of the diffracted light beams alongseveral parallel planes for the display system of FIG. 8. In contrast tothe prior art display system, as the various diffracted light beamspropagate from one plane to the next, they spread out in a directionperpendicular to the axis of the linear array 85. They become spatiallyseparated a few millimeters from the linear array 85 and remainspatially separated throughout the system, except near the screen 90 andany intermediate image planes. FIG. 12d shows the light distributionjust before the turning mirror 82 and the stop 83, which block theunwanted diffracted orders. Only the +1st and −1st order light beamspass through the projection lens system 75. For better opticalefficiency, higher diffracted orders could also be allowed through.FIGS. 12e-12 h show the +1st and −1st order light beams after they havegone through the projection lens system and pass through focus at theFourier plane (D=100 mm). Near the Fourier plane, the two first orderlight beams are tightly focused into two spots. Therefore, by placingthe scanning mirror 77 here, it can be kept small and light. The +1stand −1st order light beams overlap spatially when they finally reach thescreen 90.

An alternate embodiment of the display system is shown in FIG. 13. Theprojection lens system now consists of 3 separate lens groups 75 a, 75 band 75 c. The turning mirror 82 is placed between the first lens group75 a and the scanning mirror 77 adjacent to the first lens group 75 a.This location for the turning mirror 82 can be beneficial because thediffracted light beams are collimated along one axis in this space. Thecylindrical lens 74 axis is rotated 90 degrees with respect to thecylinder lens of FIG. 8. The scanning mirror 77 is preferably placed atthe Fourier plane (focal plane) of the first lens group 75 a. The secondlens group 75 b creates an intermediate image 92 of the linear array 85that can be used to modify the image appearing on the screen 90. Forexample, an aperture can be placed in this plane to create a sharpboundary for the image. The third lens group 75 c projects theintermediate image 92 onto the screen 90.

In the embodiments of FIGS. 8 and 13, the turning mirror 82 is used bothfor providing illumination to the linear array 85 and for blocking the0^(th) order light beam from reaching the screen 90. This requiresprecise positioning of a small turning mirror 82, which can be difficultfor the case of conformal grating devices where the diffracted ordersmay only be separated by 1 degree. Furthermore, the embodiment of FIG.13 can have a reduction in contrast of the projected image caused byweak reflections of the incident light from the first lens group 75 a.

According to the present invention, a display system that incorporates asegmented waveplate 120 can be used to eliminate these two problems asillustrated in FIGS. 14 and 15a. Referring to FIG. 14, the source 70emits linearly polarized light that is reflected by a polarizationelement, here shown as a polarization beamsplitter 96 and focuses on thelinear array 85. For optimum illumination and light efficiency, thesource is preferably a linearly polarized laser. Unpolarized sources mayalso be used since the polarization beamsplitter 96 will render thereflected light linearly polarized. Referring to FIG. 15a, the incidentlight illuminating the linear array 85 passes unmodified through thecentral portion 124 of the segmented waveplate 120. If a particulardevice on the linear array 85 of FIG. 14 is not actuated, it diffractsthe incident light beam primarily into the 0th order light beam. The 0thorder passes back through the central portion 124, hits the polarizationbeamsplitter 96 of FIG. 14 and is reflected towards the source 70 ofFIG. 14. On the other hand, if a particular device is actuated, itdiffracts the incident light beam primarily into +1st order and −1storder light beams. These two first-order diffracted light beams passthrough the half-wave segments 122 of the segmented waveplate 120 ofFIG. 16a, which then rotates the linear polarization by 90 degrees.Specifically in FIG. 14, the polarization beamsplitter 96 allows thisstate of polarization to be projected onto a screen 90 by a projectionlens system 75. Higher-order diffracted light beams can be blocked bythe addition of a stop 83 or by adding additional clear portions to thesegmented waveplate 120.

FIG. 15b shows an alternative embodiment of the segmented waveplate 120in which the central portion 124 is replaced by a full-wave segment 126.In practice this solution may be more easily manufacturable, since itcan be implemented by merely overlapping two half-wave plates. Theoptical subsystem 140 of FIG. 14 that combines the linear array 85, thesegmented waveplate 120 and the polarization beamsplitter 96 is a basicblock that can be incorporated into other types of systems. The specificexample of a printer will be discussed later. If higher efficiency isdesired, the segmented waveplate 120 can be selected so that higherorder light beams pass through the system.

The above embodiments can be used either for single color or forcolor-sequential display systems. For a color-sequential display, thelight source 70 produces a plurality of colors that are sequential intime and the controller 80 is synchronized with the light source 70. Forexample, if the light source 70 consists of three combined red, greenand blue lasers, these lasers are turned on sequentially to produceoverlapping red, green and blue images on the screen 90. The image datasent by the controller 80 to the linear array 85 is synchronized withthe turned-on laser color.

Color-sequential display systems waste two-thirds of the available lightbecause only one color is projected at a time. FIG. 16 depicts anembodiment of the invention that projects three colors simultaneously.In FIG. 16, the light source 70 emits linearly-polarized red, green andblue beams. After these three beams strike polarization beamsplitter 96,they are separated by a color combination cube 100 and are focused ontodistinct linear arrays by three projection lenses 72 r, 72 g and 72 b.Red light illuminates linear array 85 r, green light illuminates lineararray 85 g and blue light illuminates linear array 85 b. The 0^(th)order light beams emerging from the three linear arrays pass unmodifiedthrough the central portions of three segmented waveplates 120 r, 120 gand 120 b. However, the +1^(st) and −1^(st) order light beams passthrough the half-wave portions of the segmented waveplates, whichrotates the beam polarization by 90 degrees. Each of the waveplates ischosen to match the color of interest. All of the +1^(st), 0^(st) and−1^(st) order light beams are combined by the color combination cube 100and subsequently strike the polarization beamsplitter 96. Because of thedifference in the state of polarization, the polarization beamsplitter96 reflects the red, green and blue 0^(th) order beams back towards thesource and allows the red, green and blue +1^(st) and −1^(st) orderlight beams to project onto a screen 90.

Alternatively, a color-simultaneous display system can be made with asingle multi-color segmented waveplate 130 located between apolarization beamsplitter 96 and a color combination cube 100, as shownin FIGS. 17 and 18. In this embodiment, each of the linear arrays 85 r,85 g and 85 b has the same period Λ, or a period chosen so that the red,green and blue +1^(th) and −1^(st) order light beams do not spatiallyoverlap as they pass through the multi-color segmented waveplate 130.Referring to FIG. 18, the red, green and blue 0^(th) order light beamsare transmitted unmodified through a central opening 134 and arereflected towards a light source 70 of FIG. 17 by the polarizationbeamsplitter 96. The red, green and blue +1^(st) and −1^(st) order lightbeams each pass through a corresponding half-wave segment 132 r, 132 gand 132 b, which causes the beams to be projected onto the screen 90.

In practice, because color combination cubes usually only work well witha particular state of linear polarization, the embodiment of FIG. 17allows for a better design than the one of FIG. 16. In the displaysystem of FIG. 17 all of the +1^(st) and −1^(st) order light beamstraveling through the color combination cube 100 have the same state ofpolarization as their 0^(th) order counterparts. On the other hand, inthe display system of FIG. 16, the state of polarization of the +1^(st)and −1^(st) order light beams in the color combination cube 100 isrotated with respect to the 0^(th) order. Therefore, the system of FIG.16 requires good performance from the color combination cube 100 forboth states of linear polarization of each color, whereas the one ofFIG. 17 only requires good performance for a single state of linearpolarization.

The color-simultaneous display systems of FIGS. 16 and 17 each requirethree projection lens systems 72 r, 72 g, 72 b. A lower-costcolor-simultaneous display system with a single projection lens system75 is illustrated in FIG. 19.

The embodiments described above can readily be altered to obtainprinting systems. For example, FIG. 20 shows a printer that is fashionedfrom the optical subsystem 140 from FIG. 14. An imaging lens 105 is usedat finite conjugates to create a line image of a linear array 85 onlight sensitive media 110. This line image is formed from the +1^(st)order and −1^(st) order light beams that pass through the polarizationbeamsplitter 96. Although a scanning mirror 77, as shown in FIG. 14,could be used to create a two-dimensional image from the line image, itis usually preferable to use a media transport system to move the lightsensitive media 110 with respect to the line image. In FIG. 20, themedia transport system is a rotating drum 107. The motion of the mediamust be synchronized with the actuation of the electromechanicalconformal grating devices of the linear array 85 by the controller 80.This embodiment can be used for either a monochrome or acolor-sequential printer. To obtain a high-speed printer that can printthree colors simultaneously on photographic paper, three linear arrayswould be needed.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

5 a conformal grating device

5 b conformal grating device

5 c conformal grating device

5 d conformal grating device

10 substrate

12 bottom conductive layer

14 protective layer

16 standoff layer

18 spacer layer

20 ribbon layer

22 reflective, conductive layer

23 a elongated ribbon element

23 b elongated ribbon element

23 c elongated ribbon element

23 d elongated ribbon element

24 a end support

24 b end support

25 channel

27 intermediate support

28 gap

29 standoff

30 incident light beam

32 0^(th) order light beam

35 a +1^(st) order light beam

35 b −1^(st) order light beam

36 a +2^(nd) order light beam

36 b −2^(nd) order light beam

40 substrate

42 bottom conductive layer

44 protective layer

45 a GLV device

45 b GLV device

45 c GLV device

45 d GLV device

45 e GLV device

46 ribbon element

46 a movable ribbon element

46 b stationary ribbon element

48 reflective and conductive layer

50 channel

54 incident light beam

55 0th order light beam

56 incident light beam

57 +1st order light beam

58 −1st order light beam

60 a channel

60 b channel

60 c channel

60 d channel

60 e channel

62 a GLV device

62 b GLV device

62 c GLV device

62 d GLV device

62 e GLV device

70 light source

72 spherical lens

72 r projection lens

72 g projection lens

72 b projection lens

74 cylindrical lens

75 projection lens system

75 a first lens group

75 b second lens group

75 c third lens group

77 scanning mirror

80 controller

82 turning mirror

83 stop

85 linear array

85 r linear array

85 g linear array

85 b linear array

88 line of light

90 screen

92 intermediate image

96 polarization beamsplitter

100 color combination cube

105 imaging lens

107 rotating drum

110 light sensitive media

120 segmented waveplate

120 r segmented waveplate

120 g segmented waveplate

120 b segmented waveplate

122 half-wave segment

124 central portion

126 full-wave segment

130 multi-color segmented waveplate

132 r half-wave segment for red

132 g half-wave segment for green

132 b half-wave segment for blue

134 central opening

140 optical subsystem

f focal distance

What is claimed is:
 1. A display system, comprising: a light sourceproviding illumination; a linear array of electromechanical gratingdevices of at least two individually operable devices receiving theillumination wherein a grating period is oriented at a predeterminedangle with respect to an axis of the linear array wherein the angle islarge enough to separate diffracted light beams prior to a projectionlens system for projecting light onto a screen; a polarization sensitiveelement that passes diffracted light beams according to theirpolarization state; a segmented waveplate for altering the polarizationstate of a discrete number of selected diffracted light beams whereinthe segmented waveplate is located between the linear array and thepolarization sensitive element; a scanning element for moving theselectively passed diffracted light beams on the screen; and acontroller for providing a data stream to the individually operabledevices.
 2. The display system of claim 1, wherein the linear array isconstructed of electromechanical conformal grating devices.
 3. Thedisplay system of claim 1, wherein the linear array is constructed ofelectromechanical grating light valves.
 4. The display system of claim1, wherein the predetermined angle is defined to be perpendicular to theaxis of the linear array.
 5. The display system of claim 1, wherein thelinear array receives linearly polarized illumination.
 6. The displaysystem of claim 5, wherein the polarization sensitive element is apolarization beamsplitter and delivers the linearly polarizedillumination to the linear array.
 7. The display system of claim 5,wherein the segmented waveplate rotates the polarization state of thediscrete number of selected diffracted light beams by ninety degreeswith respect to the linearly polarized illumination while leaving thepolarization state of other diffracted light beams unmodified.
 8. Thedisplay system of claim 1, wherein the light source is of a singlecolor.
 9. The display system of claim 1, wherein the light sourceproduces a plurality of colors that are sequential in time and thecontroller is synchronized with the light source.
 10. The display systemof claim 1, wherein the light source produces a plurality of colors atthe same time and the display system includes a corresponding number oflinear arrays of electromechanical grating devices.
 11. The displaysystem of claim 10, wherein the segmented waveplate further includescorresponding segmented regions for altering the polarization state ofthe selected diffracted light beams for each of the plurality of colors.12. The display system of claim 1 comprising at least three lightsources and includes a corresponding number of linear arrays ofelectromechanical grating devices.
 13. The display system of claim 1,wherein the segmented waveplate selects first order diffracted lightbeams for projection onto the screen.
 14. The display system of claim 1,wherein the segmented waveplate selects a zeroth order diffracted lightbeam for projection onto the screen.
 15. The display system of claim 1,wherein the scanning element is placed at a Fourier plane of theprojection lens system.
 16. The display system of claim 1, wherein thepolarization sensitive element is simultaneously used for delivery oflight from the light source to the linear array and for passing thediscrete number of selected diffracted light beams.
 17. The displaysystem of claim 1, wherein the projection lens system includes anintermediate image plane after the scanning element wherein atwo-dimensional image is formed and is relayed to the screen.
 18. Anoptical subsystem, comprising: an electromechanical grating device thatreceives illumination from a light source; a polarization sensitiveelement for passing diffracted light beams dependent on theirpolarization state; and a segmented waveplate that alters thepolarization state of a discrete number of selected diffracted lightbeams wherein the segmented waveplate is located between theelectromechanical grating device and the polarization sensitive element.19. The optical subsystem of claim 18, wherein the electromechanicalgrating device is a conformal grating device.
 20. The optical subsystemof claim 18, wherein the electromechanical grating device is a gratinglight valve.
 21. The optical subsystem of claim 18, wherein theelectromechanical grating device receives linearly polarizedillumination.
 22. The optical subsystem of claim 21, wherein thesegmented waveplate rotates the polarization state of the discretenumber of selected diffracted light beams by ninety degrees with respectto the linearly polarized illumination while leaving the polarizationstate of other diffracted light beams unmodified.
 23. The opticalsubsystem of claim 18, wherein the polarization sensitive element is apolarization beamsplitter that delivers illumination to theelectromechanical grating device.
 24. A printing system for printing ona light sensitive medium, comprising: a light source providingillumination; a linear array of electromechanical grating devices of atleast two individually operable devices receiving the illuminationwherein a grating period is oriented at a predetermined angle withrespect to an axis of the linear array wherein the angle is large enoughto separate diffracted light beams prior to a projection lens systemthat creates an image; a polarization sensitive element that passesdiffracted light beams dependent on their polarization state; asegmented waveplate that alters the polarization state of a discretenumber of selected diffracted light beams wherein the segmentedwaveplate is located between the linear array and the polarizationsensitive element; and a controller for providing a data stream to theindividually operable devices.
 25. The printing system of claim 24,wherein the linear array is constructed of electromechanical conformalgrating devices.
 26. The printing system of claim 24, wherein the lineararray is constructed of electromechanical grating light valves.
 27. Theprinting system of claim 24, wherein the predetermined angle is definedto be perpendicular to the axis of the linear array.
 28. The printingsystem of claim 24, wherein the linear array receives linearly polarizedillumination.
 29. The printing system of claim 28, wherein thepolarization sensitive element is a polarization beamsplitter thatdelivers the linearly polarized illumination to the linear array. 30.The printing system of claim 28, wherein the segmented waveplate rotatesthe polarization state of the discrete number of selected diffractedlight beams by ninety degrees with respect to the linearly polarizedillumination while leaving the polarization state of other diffractedlight beams unmodified.
 31. The printing system of claim 24, wherein thelight source is of a single color.
 32. The printing system of claim 24,wherein the light source produces a plurality of colors that aresequential in time and the controller is synchronized with the lightsource.
 33. The printing system of claim 24, wherein the light sourceproduces a plurality of colors at the same time and the printing systemincludes a corresponding number of linear arrays of electromechanicalgrating devices.
 34. The printing system of claim 24, wherein thesegmented waveplate further includes corresponding segmented regionsthat alter the polarization state of the selected diffracted light beamsfor each of the plurality of colors.
 35. The printing system of claim 24comprising at least three light sources and includes a correspondingnumber of linear arrays of electromechanical grating devices.
 36. Theprinting system of claim 24, wherein the segmented waveplate selectsfirst order diffracted light beams for printing on the light sensitivemedium.
 37. The printing system of claim 24, wherein the segmentedwaveplate selects a zeroth order diffracted light beam for printing onthe light sensitive medium.
 38. The printing system of claim 24, whereinthe polarization sensitive element simultaneously delivers light fromthe light source to the linear array and passes the discrete number ofselected diffracted light beams.